The present invention relates to the field of nickel-plating by means of nickel-plating baths using nickel sulfamate as the nickel-providing compound, and provides a method of regenerating such baths. A particularly important application of the invention lies in regenerating nickel-plating baths used for plating structural components of a nuclear power station, in particular certain zones in the tubes of steam generators, such as those used in pressurized water reactors.
It is known that nickel-plating of the inner surfaces of the U-shaped regions of the tubes in a steam generator, i.e., the regions where the tubes are subjected to particularly high stresses, may close microcracks or prevent such cracking from taking place. For an example of a nickel-plating repair method, reference may be made to EP-A-0 167 513.
It is conventional to use nickel-plating baths in which the nickel-providing ingredient is nickel sulfamate. These baths suffer from the drawback of oxidizing and of causing fast passivation of anodes.
Boric acid has also been used to achieve an optimum pH, essential for obtaining good electrochemical conditions for nickel-plating and to avoid decomposition of nickel sulfamate due to hydrolysis.
Proposals have further been made to avoid anode passivation by adding chloride to the bath.